As the amount of mobile data traffic is constantly growing, spectrum resources become increasingly insufficient, and a demand for the amount of traffic may have been not satisfied using licensed spectrum resources alone for network deployment and traffic transmission, so the transmission can be deployed on unlicensed spectrum resources in a Long Term Evolution (LTE) system to improve the experience of a user and to extend a coverage area.
(1) Downlink Data Transmission Schemes
In the LTE system, a UE operates on only one carrier; and in a Long Term Evolution-Advanced (LTE-A) system, the UE can operate concurrently on N carriers. Downlink data on each of the carriers are retransmitted through scheduling by a Physical Downlink Control Channel (PDCCH), and transmission sub-frames and retransmission configurations (including a transmission bandwidth, a Modulation and Coding Scheme (MCS), and other parameters) of the retransmitted data can be adjusted flexibly by the scheduling PDCCH. Different data transmission is identified by different Hybrid Automatic Repeated Request (HARQ) processes, and initial transmission and retransmission of the same data correspond to the same HARQ process. The HARQ processes on the different carriers are indexed separately, and indicated by an HARQ process number field in Downlink Control Information (DCI) formats for the PDCCH scheduling the carriers.
For a carrier operating in the Frequency Division Duplex (FDD) mode, the maximum number of downlink HARQ processes on each carrier is 8, that is, at most 8 downlink HARQ processes can coexist on an FDD carrier, so that 8 different data transmission processes can coexist, and there are N*8 downlink HARQ processes in total on N FDD carriers. Thus the HARQ process number field in the DCI format of the FDD system includes 3 bits of information, where 8 different combination states of the 3 bits of information indicate process indices of the 8 HARQ processes on a carrier respectively, and the 3-bit HARQ process number field in the DCI format for the PDCCH scheduling the carrier indicates one of the 8 HRAR processes on the carrier, to which the currently scheduled data correspond.
For a carrier operating in the Time Division Duplex (TDD) mode, the maximum number of downlink HARQ processes on each carrier depends upon a TDD uplink/downlink configuration as depicted in Table 1, where multiple carriers are configured or aggregated for the UE, and different TDD uplink/downlink configurations are applied to the multiple carriers; and the TDD uplink/downlink configuration in Table 1 is a downlink reference TDD uplink/downlink configuration of the carrier. If all the TDD uplink/downlink configurations of N aggregated TDD carriers are configured with the TDD uplink/downlink configuration 5, then there will be N*15 downlink HARQ processes in total. Thus there are 4 bits of information in the HARQ process number field in the DCI format of the TDD system, where X combination states among 16 different combination states of the 4 bits of information indicate process indices of X HARQ processes on a TDD carrier respectively, where X<=15; and the 4-bit HARQ process number field in the DCI format for the PDCCH scheduling the carrier indicates one of the X HARQ processes on the carrier, to which the currently scheduled data transmission corresponds.
Moreover for FDD and TDD carriers, there are also a New Data Indicator (NDI) field and a Redundancy Version (RV) field in the DCI format for the PDCCH scheduling the carrier, where the NDI field includes 1 bit of information to indicate whether the current data transmission scheduled by the PDCCH is initial transmission or retransmission, and the RV field includes 2 bits of information to indicate one of the versions 0 to 3, which is applied to the RV of the data for the current transmission scheduled by the PDCCH, where both of these two fields correspond to the HARQ process number field, that is, both of the fields indicate information about the data transmission in the HARQ processes indicated by the HARQ process number filed in the PDCCH.
TABLE 1Maximum number DL HARQ processes for TDDTDD UL/DLMaximum number ofconfigurationHARQ processes04172103941251566
(2) Unlicensed Spectrums
The existing spectrums can be categorized into licensed spectrums and unlicensed spectrums, where the licensed spectrums are allocated dedicated spectrums, and interference thereof is substantially predicable; and there are no particular planed systems to which the unlicensed spectrums are applicable, and they can be shared by a number of systems, e.g., LTE, WiFi, etc., so interference thereof may not be predicable, and the transmission performance and the quality of service of data transmission thereof may not be determinate, where if there is low interference, then the transmission performance and the quality of service may be acceptable, and if there is high interference, then the performance of data transmission may be lowered, and the quality of service may be degraded.
Thus if the LTE system operates on an unlicensed spectrum resource, then there may be unpredictable interference so that the performance of data transmission on a carrier operating on the unlicensed spectrum resource may be poor, thus discouraging the throughput of the system.
There has been absent so far a working solution to the problem of to v transmission performance of the system operating on an unlicensed spectrum resource in the prior art.